This invention relates to hydrocarbon plasticizers for polypropylene thermoplastics.
The blending of plasticizers in general with thermoplastics and the resulting plasticization of those thermoplastics are well known and many reviews have been written. A plasticizer is generally an organic compound incorporated into a high polymer, such as for example a thermoplastic, to desirably facilitate processing, increase its workability, flexibility, and/or distensibility of the polymer.
Within the last few years efforts have been made in the field of plasticizers to better understand factors which govern plasticizer/thermoplastic miscibility. Examples of a thermoplastic and plasticizer include polypropylene and low molecular weight polyolefins, respectively. Polypropylene is an inexpensive polyolefin engineering thermoplastic that is generally stiff and even brittle below room temperature especially for highly stereoregular polypropylene. Tackifiers are examples of low molecular weight polyolefins plasticizers. Examples of tackifiers include hydrocarbon resins derived from fractionated petroleum distillates, coal tar, turpentine fractions and from copolymerization of pure aromatic monomers. However, these tackifiers typically have high glass transition temperature (Tg) and high solubility parameter. As such, upon blending, these tackifiers tend to raise the Tg of the polypropylene. Increasing the Tg increases the stiffness of polypropylene.
Other plasticizers, which have low Tg, (below xe2x88x9220xc2x0 C.) such as ethylene-propylene rubber, ethylene-butene copolymer (having a Mw greater than or equal to 20,000), are immiscible with the polypropylene. Plasticizers which are immiscible with polypropylene tend to collect on the surface of the manufactured article, hinder the manufacturing process of articles made therefrom and may cause the resulting product to have generally undesirable features.
Because polypropylene is an inexpensive thermoplastic, there exists a need to improve its workability and to overcome its inherent stiffness and brittleness which limit its commercial application. Therefore, a need exist to safely and economically improve the workability, flexibility, and/or distensibility of polypropylene.
Miscible blends of polypropylene with low molecular weight ethylene xcex1-olefin copolymer plasticizers have been discovered. By blending such miscible, low molecular weight ethylene xcex1-olefin copolymer plasticizers with polypropylene (isotactic polypropylene, syndiotactic polypropylene and atactic polypropylene), the glass transition temperature, storage modulus and viscosity of the blended polypropylene are lowered. By decreasing the glass transition temperature, storage modulus and viscosity, the workability, flexibility, and distensibility of polypropylene improves. As such, broadened commercial application for these new polypropylene blends in film, fibers and molded products is apparent. Furthermore, the flexibility of a product design utilizing these novel blends can be further extended by taking advantage of the enhanced comonomer incorporation and tacticity control possible with metallocene catalysts, both of which can reduce isotactic polypropylene (xe2x80x9ciPPxe2x80x9d) crystallinity prior to blending with the low molecular weight ethylene a-olefin copolymer plasticizers.
In one embodiment, a plasticized polypropylene thermoplastic is provided. The plasticized polypropylene thermoplastic includes from 50 to 99.9 weight percent (xe2x80x9cwt %xe2x80x9d) of a thermoplastic polymer derived from polypropylene. Optionally, the thermoplastic polymer is copolymerizable with one or more monomers selected from C2-C10 xcex1-olefin or diolefin. The thermoplastic polymer desirably has a melt flow rate (MFR) (ASTM D1238) in the range of from 0.3 to 1000 and a crystallinity, determined by differential scanning calorimetry (DSC) at a scan rate of 10xc2x0 C. per minute, in the range of from 0 to 70% crystallinity. The thermoplastic polymer is blended with from 0.1 to 50 wt % of at least one ethylene copolymer. The ethylene copolymer desirably has a weight-average molecular weight (Mw) (GPC) of from 500 to 10,000, a molecular weight distribution (MWD) (GPC) of from greater than 1.5 to less than or equal to 3.5, and a comonomer content of from greater than or equal to 20 mol % to less than 70 mol %. The plasticized polypropylene thermoplastic may include from 0 to 20 wt % of the polypropylene thermoplastic composition, of a thermoplastic polypropylene modifier compound other than the ethylene copolymer described above. Examples of thermoplastic polypropylene modifier compounds include one or more compositions selected from the group which includes antioxidants, fillers, pigments, hydrocarbon resins, rosins or rosin esters, waxes, UV stabilizers, additional plasticizers, and tackifiers such as ESCOREZ, a product of Exxon Chemical, which is more fully described in U.S. Pat. No. 5,317,070 which is incorporated by reference herein. Additionally, the terminal vinylidene groups present on some of the above thermoplastic polypropylene modifier compounds may be functionalized, such functionalization being more fully described in U.S. Pat. Nos. 5,763,556 and 5,498,809, both of which are incorporated by reference herein.
The ethylene copolymer may be further described as having a glass transition temperature (Tg) of from greater than or equal to xe2x88x9280xc2x0 C. to less than or equal to xe2x88x9230xc2x0 C. In another embodiment, the ethylene copolymer may be described as having an ethylene crystallinity, as determined by differential scanning calorimetry (DSC) at a scan rate of 10xc2x0 C. per minute of less than or equal to 5% crystallinity.
In another embodiment, the plasticized polypropylene thermoplastic may be further described as having a crystallinity by DSC at a scan rate of 10xc2x0 C. per minute of less than 60% and wherein the wt % of said ethylene copolymer present in the plasticized polypropylene thermoplastic is less than or equal to y, wherein y is in the range of 0.1 to 50, as determined by y in the equation
y=50xe2x88x920.5x
where x=the % crystallinity of the thermoplastic polymer.
In another embodiment, the thermoplastic polymer may be further described as having a crystallinity by DSC at a scan rate of 10xc2x0 C. per minute of greater than or equal to 60% and wherein the wt % of said ethylene copolymer present in the plasticized polypropylene thermoplastic can be as high as 20.
In another embodiment, the ethylene copolymer component may include, in addition to ethylene, one or more of C3 to C20 linear or branched xcex1-olefin or diolefin. Desirably, the ethylene copolymer may be either an ethylene-propylene, ethylene-butene copolymer, ethylene-hexene copolymer, ethylene-octene copolymer, ethylene norbornene, ethylene styrene copolymers, and ethylene-isobutylene copolymers or mixed monomers including ter-, tetrapolymers, and the like, thereof.
In another embodiment, a plasticized polypropylene thermoplastic composition is provided which includes a blend of a thermoplastic polymer and the ethylene copolymer. The thermoplastic polymer is desirably derived from amorphous propylene. Desirably, from 50 to 99.9 wt % of the plasticized polypropylene thermoplastic is the thermoplastic polymer. Optionally the thermoplastic polymer may include one or more copolymerizable monomers selected from C2-C10 xcex1-olefin or diolefin. The thermoplastic polymer has melt flow rate (MFR) (ASTM D1238) in a range from 0.3 to 1000 and a crystallinity, as determined by differential scanning calorimetry (DSC at a scan rate of 10xc2x0 C. per minute), in a range from 0 to less than 5%. Desirably, from 0.1 to 50 wt % of the plasticized polypropylene thermoplastic is the ethylene copolymer. The ethylene copolymer has a weight-average molecular weight (Mw) (GPC) in a range from 500 to 10,000, a molecular weight distribution (MWD) (GPC) in a range from greater than 1.5 to less than or equal to 3.5, and a comonomer content in a range from greater than or equal to 20 mol % to less than 70 mol %. The plasticized polypropylene thermoplastic may also include from 0 to 20 wt % thereof of a thermoplastic polypropylene modifier compound other than the ethylene copolymer. Examples of this thermoplastic polypropylene modifier include, but are not limited to, antioxidants, fillers, pigments, hydrocarbon resins, rosins or rosin esters, waxes, UV stabilizers, additional plasticizers, singularly or in combination.
In another embodiment, the plasticized polypropylene thermoplastic may be further described as having a crystallinity by DSC at a scan rate of 10xc2x0 C. per minute of less than 5% and wherein the wt % of said ethylene copolymer present in the plasticized polypropylene thermoplastic is less than or equal to y, wherein y is in the range of 0.1 to 50, as determined by y in the equation
y=50xe2x88x920.5x
where x=the % crystallinity of the thermoplastic polymer.
In another embodiment, a plasticized polypropylene thermoplastic composition is provided which includes a blend of a thermoplastic polymer and the ethylene copolymer wherein the wt % of the ethylene copolymer in the plasticized polypropylene thermoplastic is less than or equal to y, wherein y is in the range of 0.1 to 50, as determined by y in the equation
y=50xe2x88x920.5x
where x=the % crystallinity of said thermoplastic polymer. The thermoplastic polymer is derived from polypropylene, optionally with one or more copolymerizable monomer selected from C2-C10 xcex1-olefin or diolefin, said thermoplastic polymer having a melt flow rate (MFR) (ASTM D1238) of from 0.3 to 1000. The ethylene copolymer has a weight-average molecular weight (Mw) (GPC) of from 500 to 10,000, a molecular weight distribution (MWD) (GPC) of from greater than 1.5 to less than or equal to 3.5, and a comonomer content of from greater than or equal to 20 mol % to less than 70 mol %. In one embodiment, from 50 to 99.9 wt % of the plasticized polypropylene thermoplastic is derived from the thermoplastic polymer and from 0.1 to 50 wt % of the plasticized polypropylene thermoplastic is derived from the ethylene copolymer. Desirably, the crystallinity, by differential scanning calorimetry (DSC at a scan rate of 10xc2x0 C. per minute), of the thermoplastic polymer is in a range of from 0 to 70%.
In another embodiment, a plasticized polypropylene thermoplastic composition formed from a blend of a thermoplastic polymer and an ethylene copolymer is provided. The thermoplastic polymer derived from polypropylene, optionally with one or more copolymerizable monomer selected from C2-C10 xcex1-olefin or diolefin, said thermoplastic polymer having a melt flow rate (MFR) (ASTM D1238) of from 0.3 to 1000. The ethylene copolymer has a weight-average molecular weight (Mw) (GPC) of from 500 to 10,000, a molecular weight distribution (MWD) (GPC) of from greater than 1.5 to less than or equal to 3.5, and a comonomer content of from greater than or equal to 20 mol % to less than 70 mol %. The wt % of the ethylene copolymer in the thermoplastic composition is less than or equal to y, wherein y is in the range of 0.1 to 50, as determined by y in the equation
y=50xe2x88x920.5x
where x=the % crystallinity of said thermoplastic polymer.